New Form of Li2FePO4F as Cathode Material for Li-Ion Batteries

The synthesis employed for obtaining the pure NaLiFePO4F phase, its structure determination, and electrochemical activity was reported. Fluorophosphate NaLiFePO4F was prepared by annealing a stoichiometric mixture of LiFePO4 and NaF at 650-700°C for 2 h under Ar-flow. The carbon-containing composite NaLiFePO4F/C was prepared by adding a carbon black to the initial mixture. The X-ray diffraction (XRD) pattern of the obtained gray powder was fully indexed in the Pnma space group with cell parameters. The structure of NaLiFePO4F was determined by Rietveld refinement of the XRD pattern using the structural model of Li2NiPO4F as a first approach. The fractional coordinates and displacement parameters of the atoms were refined along with the occupancy of the three alkali sites. Electrochemical testing on the carbon coated NaLiFePO4F sample revealed a promising electrode material, which exhibits a sloping profile with an average potential of 3.4 V vs Li.